Faced with a no start condition?

Carefully clean the ground studs (3 total) behind your head lights before (like me) overthinking things!

So, my 07 XJR (108K miles) got flatbedded home friday, having jerked, sputtered, restarted, and finally quit about 3 miles from home. I was pretty sure the problem was fuel related, and dismayed to find that a flat battery (emer flashers, plus trying to restart) had caused (I thought) the PCM to log about every DTC under the sun (except fuel related).

In the driveway, battery charged, the engine would start normally, then immediately die. Fuel pressure, however, remained about 55 - 60 psi even after it died, and remained about 45 psi overnight (according to my cheapie Foxwell scanner reading the fuel rail pressure sensor via live data). Yes, I know the SC max fuel pressure spec is 70 psi, but I believe this is under full load duty cycle, not idling

Researching old threads on this forum, I found one (Don B - the best, most helpful thread author we have, IMHO) where a fellow in Germany was having his XJ8 cut out when he turned on the wipers. Turned out to be a corroded lower grounding stud behind the RH headlight housing. While I had cleaned the LH stud while reringing my suspension compressor last summer, I went ahead and cleaned the two RH studs (just for grins - even though they looked clean, even shiny). Bingo! Car starts and runs normally now.

I suspect that the crank sensor (CKP) may be failing (or connector is iffy), and cleaning up the ground point may have temporarily returned it to its duty. I'll lift the car tomorrow and check it out. The good news is that its cheap, while the XJR fuel pump ain't. BTW, a 4 mile roadtest failed to throw any PCM codes at all


BTW, to clean the ground points, I used a brass toothbrush, then rinsed with aerosol contact cleaner, then daubed with deox grease, and finally snugged things back up. These are AL studs, nuts, and connectors, so don't overtighten (or you'll break the stud). I used a thin 13mm open end wrench

Aluminum conducts electricity well, but it tends to form an insulating coating (actually, an oxide film). So, one small downside of our AL cars is the need to maintain ground points which are exposed to weather. I don't believe Jag used any deox grease at the factory on these little buggers...

 

Yep - The X350 XJ's and XF's X250 have similar issues with the ground studs below headlamps.


Have also seen issues with the ground studs in the front wheel wells as well, specially on XK X150's...

 

So, I pulled the CKP (crank sensor). Everything clean; a little ring gear swarf on sensor end. Cleaned contacts, etc and reinstalled, Ditto the cam sensors, just because...

I'm going to order a CKP and replace, just to be safe

I've now driven the car about ten miles, with plenty of restarts, and it seems fine. Also, the CEL (cat efficiency) I've had since buying the car two years ago has not reilluminated, plus no other DTC so far. This is inconclusive, but I'll report back after another 100 miles or so

It snowed over the weekend here, and so I studied a bunch of forum threads and missed church Those with resolved notes (unfortunately, only maybe 5%) showed ground problems as a common denominator fairly often, sometimes after ECU replacement and a lot of other pain

So, men, go clean your grounds!

 

Hi John,

Thank you for your kind words! I'm sure I'm blushing, but I'm just trying to pay forward all the help I've received myself from the amazingly knowledgeable and generous members of our Jaguar community, including you!

Regarding engine bay grounds, don't forget the main ground referenced by the ECM, which is under the front edge of the cabin air microfilter housing behind the right front air spring/shock tower. And also the engine ground strap.

In the trunk, the ground referenced by the REM is important (on the right rear inner wheel well behind the right carpeted trim panel which is easy to pull out), as are the two battery negative cable grounds and the ground near the RPDFB.

Regarding DE-OX Oxide Inhibitor, for those who may not know about these types of products, IMHO it is best to not apply any type of grease on any connector terminal pins or ground nut/stud/eyelets while they are apart, because even conductive grease products add resistance that can affect sensitive sensor and multiplex network signals (dielectric grease is non-conductive).

Instead, for grounds, I clean and reinstall the wire terminals and nuts (torqued to just 6.5 ft. lbs. per the manual), then apply grease to the exposed edges of the wire eyelet/ring terminals and base of the stud, and to the end of the threaded stud. For electrical connectors, I do not apply grease on any connector pins, but only around the outside of the inner half of the connector to promote an air-tight seal when the two halves are reconnected (I think I recall that this is how DE-OX recommends their Oxide Inhibitor be used).

Cheers,

Don

 

Thanks, Don

Funny, I was about to try looking up the location of other ground points in the mind numbing Jag service manual (which, BTW, is published by the Department of Redundancy Department)

Having now got religion, I'm going to clean up all these points also. Appreciate the tip

Regarding deox, I used to be super careful not to get it between conductors, at least until an electronics guy gave me a dope slap and said "That's where it belongs, stupid". His rationale is that the grease is displaced by metal to metal contact, and, in turn, isolates that contact area from atmosphere, moisture, etc. This, of course, does not apply to any make/break contacts (eg, relay contacts). I'm working on my (Japanese) Kubota tractor right now, and all the electrical connectors are bathed in deox grease. I'm surprised they don't have zerk fittings...

john

PS:

The whole grounding thing is sorta' metaphysical to me, having - at age 12 or so - raised the bonnet on our neighbors MGB, only to see "Caution: Positive Earth" emblazoned within. I figured that Positive Earth must be the secret ingredient in all truly cool cars.

My neighbor had earlier recruited me to occasionally crawl under the MG with the (knock off) mallet and whack the SU fuel pump until it began ticking again. This time, however, it was to find the battery (we went about discovering two of 'em, behind the rear "seat" somewhere).
As the MG (and I) got older, I ended up discovering all types of other interesting and philosophical things (eg, why SU carbs are of the "Constant Depression" type, why Joesph Lucas was born the "Prince of Darkness", etc).
I blame this early childhood trauma on my lifelong fixation with metaphysics, lost causes, and old cars/motorcycles.
It is why, beyond all reason, I bought a retro looking old Jag XJR

 

Utilize Gardner-Bender OxGard in the connection for grounds. It's specific for aluminum.

 

Just be careful when cleaning the aluminium studs behind the right hand head lights - I snapped one off and had to put the 4 lugs on the remaining stud!